RU2340970C1 - Super-conducting cable - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering, particularly to super-conducting cable capable to absorb thermal compression of super-conducting wire. Super-conducting cable comprises a super-conducting wire coiled to form a super-conducting layer (layer-conductor) (13), reverse conductor (17), a layer of strain relaxation (12), an insulating layer or an outer strain relation layer (16) arranged on the super-conducting layer outer side and cable carcass, (11) arranged on the strain relaxation layer inner side.

EFFECT: superconducting layer compression absorption by cooling superconducting wire with coolant.

9 cl, 4 dwg, 1 tbl

Description

Technical field

[0001] The present invention relates to a superconducting cable. The invention, in particular, relates to a DC superconducting cable capable of absorbing thermal compression of a superconducting wire.

State of the art

[0002] As a superconducting cable, the superconducting cable shown in FIG. 4 has been proposed. The superconducting cable 100 is constructed in a structure comprising three cable cores 10 inside a heat insulating pipe 20 (see, for example, Patent Reference 1, Patent Reference 2).

[0003] The cable core sequentially from its center includes a frame 11, a conductive layer 13, an insulating layer 16A, a shielding layer 17A, a protective layer 18. The conductive layer 13 is formed by spiral winding of the superconducting wire in many layers. Usually, a tape-shaped superconducting wire is used in which a plurality of lengths of fibers containing oxide superconducting material are arranged in a silver cladding matrix or the like. An insulating layer 16A is formed by winding insulating paper. The shielding layer 17A is formed by spiral winding of the superconducting wire like a conductive layer 13 over the insulating layer 16A. In addition, insulating paper or the like is used for the backing layer 18.

[0004] In addition, the insulating tube 20 is constructed having a structure in which an insulating element (not shown) is located between the twin pipes containing the inner pipe 21 and the outer pipe 22, and the inside of these twin pipes is evacuated. A corrosion resistant layer 23 is formed on the outside of the heat insulating pipe 20. In addition, the application state is a state in which the refrigerant is in the form of liquid nitrogen or the like. it fills and circulates through the space formed inside the frame 11 (in the case when it is hollow) or between the inner pipe 21 and the core 10, and the refrigerant is impregnated into the insulating layer 16A.

[0005] Patent reference 1:

Japanese Patent Laid-Open Publication: JP-A-2003-249130 (FIG. 1)

Patent reference 2:

Japanese Patent Laid-Open Publication: JP-A-2002-140944 (FIG. 2)

Disclosure of invention

Problems Solved by the Invention

[0006] Meanwhile, in the above-described superconducting cable, in operation, the superconducting wire is cooled by the refrigerant to an extremely low temperature, thereby being compressed, and therefore, a structure with absorption of the magnitude of this compression is required. However, no simple structure was found as a mechanism for absorbing the magnitude of compression.

[0007] Although, according to a structure including 3 cable cores, a countermeasure can be taken to absorb compression by loosening twisted cores, in the case of a superconducting cable with a single core, such a countermeasure cannot be taken. Therefore, it is possible to combat this by allowing mechanical stress to act on the superconducting wire in accordance with compression during cooling, or by sliding the peripheral end portion of the superconducting cable in accordance with the thermal compression of the cable.

[0008] However, in the first case, the compression stress is allowed to act on the superconducting wire and, therefore, there is a case in which, depending on the intensity of the voltage, strong tension occurs in the superconducting wire, the superconducting wire is destroyed, or lateral pressure in the bent part of the cable acts on the heat-insulating pipe in accordance with the compression of the cable, reducing the heat-insulating function. In the latter case, however, a mechanism is required for sliding the peripheral end of the superconducting cable, and large-scale measures to counter compression are necessary. In particular, anti-compression measures using a sliding mechanism are not suitable for a long superconducting cable line connected by a plurality of superconducting cables via connections.

[0009] The present invention has been created in view of the above situation, and its main task is to create a superconducting cable capable of absorbing the magnitude of the compression of the superconducting wire during cooling with a simple structure.

[0010] Furthermore, it is another object of the invention to provide a DC superconducting cable capable of absorbing the compression amount of the superconducting wire upon cooling with a simple structure.

[0011] In addition, it is another object of the invention to provide a superconducting cable capable of absorbing the magnitude of the compression of the superconducting wire during cooling with a simple structure, and also allowing reducing the amount of used superconducting wire as much as possible.

Means for solving these problems

[0012] The invention solves the above problem by imparting a thermal compression mechanism to the superconducting layer directly to the cable core.

[0013] According to the invention, a superconducting cable is provided, comprising: a superconducting wire constituting a superconducting layer by spiral winding, and a stress relaxation layer provided on an inner side of the superconducting layer, wherein a compression amount in the diameter direction of the superconducting layer in accordance with cooling of the superconducting wire the refrigerant is absorbed by the stress relaxation layer.

[0014] By providing a stress relaxation layer on the inner side of the superconducting layer when the superconducting wire is compressed during cooling, excessive stretching of the superconducting wire can be eliminated by absorbing at least a portion corresponding to a compression amount of the diameter of the superconducting layer (a value by which diameter spiral wound superconducting wire is reduced when cooling) in accordance with this compression.

[0015] A constituent element of a superconducting cable according to the invention will be explained in detail below.

[0016] The superconducting cable according to the invention typically consists of a cable core and a heat-insulating pipe containing this cable core. Of these, the cable core is designed with a basic structure, including a stress relaxation layer, a conductor layer, an insulating layer. Typically, the cable core is provided with a frame forming the cable component. Otherwise, an outer conductor layer (shielding layer), a coil-holding layer, a shock-absorbing layer may be provided.

[0017] The frame is designed to support a conductor layer having a predetermined shape, and a tape-shaped element formed having a tubular shape or helically or a structural element having a twisted wire structure can be used. As its material, a non-magnetic metallic material of copper, aluminum or the like is preferable. Otherwise, various plastic materials may also be used. When the frame is tubular, it is preferable to form it from a corrugated tube in terms of flexibility. In the case where the frame has a tubular shape, the interior of this frame may form a channel for the flow of refrigerant.

[0018] The stress relaxation layer is a layer designed to absorb the thermal compression amount of the superconducting layer. The superconducting layer is a layer formed by spiral winding of the superconducting wire, and includes a conductor layer or an outer conductor layer (shielding layer), as mentioned above. The superconducting layer is thermally compressed when cooled by refrigerant to an extremely low temperature during cable operation. In accordance with the thermal compression of the superconducting wire, compression also occurs in the diameter direction, and therefore, when the stress relaxation layer provided on the inside of the superconducting layer is compressed corresponding to the thermal compression of the superconducting wire, the operation of the superconducting wire may be limited by excessive tension.

[0019] A stress relaxation layer may be provided with a compression amount capable of absorbing at least a portion of the compression amount of the diameter of the superconducting layer when it is exposed to extremely low temperature by the refrigerant. That is, the stress relaxation layer may be formed so as to absorb the compression amount of the superconducting layer in the diameter direction in accordance with cooling by the stress relaxation layer and the cable component provided on the inside of the stress relaxation layer, or may be formed so as to absorb the compression amount of the superconducting layer in the direction of the diameter in accordance with cooling only by the stress relaxation layer.

[0020] In the first case, the compression of the superconducting layer is absorbed by compressing both the stress relaxation layer and the cable constituent element, and therefore, the stress relaxation layer itself can be thinner. As a typical example of a cable constituent element provided on the inner side of a stress relaxation layer, a frame is indicated. In the latter case, the compression amount of the diameter of the superconducting layer is absorbed by the stress relaxation layer, and therefore, the material or structure of the constituent element on the inner side of the stress relaxation layer, for example, the frame, can be freely selected.

[0021] The location of the stress relaxation layer is on the inside of the superconducting layer. For example, it is possible to provide a stress relaxation layer on the inner side of the conductor layer (on the outer side of the chassis) as a stress relaxation layer on the inside or provide a stress relaxation layer on the inside of the outer conductor layer (shield layer) as the outer stress relaxation layer. When a stress relaxation layer is provided on the inner side of the outer conductor layer, an insulating layer per se may be used, or the stress relaxation layer may be formed separately, in addition to the insulating layer. When the insulating layer itself is used as a stress relaxation layer on the outside, it is not necessary to provide a different stress relaxation layer than the insulating layer in order to facilitate a small cable core diameter.

[0022] At least one of kraft paper, plastic tape, and a composite tape of kraft paper and plastic tape may preferably be used as the material constituting the stress relaxation layer. As the plastic tape, a polyolefin, in particular polypropylene, tape can preferably be used. Although kraft paper is usually inexpensive, the amount of compression during cooling is small, and although the composite tape made from kraft paper and polypropylene is expensive, the amount of compression during cooling is large. In particular, in the case of a composite tape, when a composite tape having a large polypropylene thickness is used, a large compression ratio can be guaranteed, and even when the compression ratio of the diameter of the superconducting wire is large, a stress relaxation layer can be formed without applying excessive tension to the superconducting wire. Otherwise, as kraft paper, corrugated kraft paper or wetted kraft paper can guarantee a large amount of compression. In addition, a stress relaxation layer having a thickness capable of absorbing at least a portion of the compression amount of the diameter of the superconducting wire may be formed by these materials individually or in combinations.

[0023] The conductor layer is a conductive portion formed by a superconducting wire. For example, a conductor layer is formed by spiral winding a superconducting wire on the outside of the carcass in several layers. As a specific example of a superconducting wire, a tape-shaped superconducting wire is provided in which a plurality of lengths of fibers containing an oxide superconducting material of a Bi2223 phase are arranged in a silver cladding matrix or the like. The superconducting wire may be wound in one layer or in several layers. In addition, when several layers are formed, an interlayer insulating layer may be provided. As an interlayer insulating layer, an interlayer insulating layer provided by winding insulating paper from kraft paper or the like, or PPLP composite paper (manufactured by Sumitomo Denki Kogyo K.K., registered trademark) or the like is indicated.

[0024] The insulating layer is formed from an insulating material having a withstand insulation voltage corresponding to the voltage of the conductor layer. For example, at least one of kraft paper, plastic tape, and a composite tape of kraft paper and plastic tape may be preferably used.

[0025] Among the corresponding above materials, the structure with the formation of an insulating layer of only kraft paper has the lowest cost. When the composite tape and kraft paper are used together, compared with the case of forming the insulating layer only from the composite tape, the amount of expensive composite tape used can be reduced and the cost of the cable can be reduced.

[0026] In particular, when a composite tape obtained by laminating kraft paper and polypropylene is used, it is preferable to use a composite tape having a ratio k of the thickness of the polypropylene film to the entire thickness of the composite tape of 60% or more. Due to the difference in the specific resistances of kraft paper and the polypropylene film constituting the composite tape, the electric field strength is largely attributable to a plastic film that is excellent in withstanding voltage characteristics. Therefore, by increasing the fraction of the plastic film occupied in the insulating layer, the withstand voltage characteristic (in particular, withstand constant voltage characteristic) of the insulating layer can be improved, and the thickness of the insulating layer can be reduced.

[0027] In addition, when the outer conductor layer indicated below is provided, it is preferable to use the insulating layer itself as the stress relaxation layer. Although the stress relaxation layer can be formed separately from the insulating layer, by using the insulating layer as such as the stress relaxation layer to absorb the compression amount of the diameter of the outer conductor layer, it is possible to limit the increase in the outer diameter of the superconducting cable.

[0028] Alternatively, a semiconducting layer may be formed on at least one of the inner and outer periphery of the insulating layer, that is, between the conductor layer and the insulating layer or between the insulating layer and the shielding layer. When forming the inner semiconducting layer in the first case and the outer semiconducting layer in the latter case, the electrical function is effectively stabilized.

[0029] An outer conductor layer may be provided on the outer side of the insulating layer. In particular, in a DC superconducting cable, the outer conductor layer is a structure necessary for transmitting electric power to a single-pole system. While a shielding layer is required in the superconducting AC cable to shield the magnetic flux flowing to the outer periphery of the conductor layer in order to reduce AC losses in the superconducting wire, the return line conductor should be formed by the outer layer in the superconducting DC cable a conductor in the area corresponding to the shielding layer of the superconducting AC cable. That is, by providing an outer conductor layer (return line conductor) comprising a superconducting wire, on the outer side of the insulating layer, the conductor layer can constitute a forward current path in a single-pole power transmission, and the outer conductor layer can be used as a reverse path current path. The outer conductor layer must be carried out with a structure having the same maximum permissible current as the maximum permissible current of the conductor layer. In addition, the superconducting cable may be a multi-core type containing a plurality of cores in an insulating pipe, and a single-pole power transmission system or a two-pole power transmission system may also be used. In the latter case, the outer conductor layer in the cable according to the invention is given the function of a neutral wire.

[0030] It is preferred that the winding pitch of the superconducting wire constituting the conductor layer or the outer conductor layer is 4-6 times larger than the diameter of the winding of the superconducting wire. The diameter of the winding is the diameter of the element wrapped in a superconducting wire, that is, the inner diameter of the layer formed by the superconducting wire. By limiting the ratio of the winding pitch to the winding diameter, as described above, it is possible to obtain a short pitch that can reduce the amount of wire compression when the superconducting wire is compressed during cooling, and obtain a winding pitch that can also limit the amount of superconducting wire used.

[0031] In the superconducting AC cable, in order to reduce AC losses by making the currents of the respective layers of the superconducting wire wound in several layers the same (formation of the same currents), the winding pitch of the superconducting wire in the respective layers is controlled. For example, a short step through a long step is combined in a range that does not damage the superconducting wire during winding of the superconducting wire and bending of the core. Therefore, the limitation on the selection of the winding pitch is significant.

[0032] On the other hand, in the case of a superconducting DC cable, it is not necessary to take into account the formation of the same current, and therefore the limitation on the choice of the winding pitch is not significant, the winding pitch can be selected relatively freely, and all layers can be wound with the same pitch .

[0033] When the winding pitch of the superconducting wire decreases, the compression amount in diameter when the superconducting wire is compressed during cooling, that is, the amount to be absorbed by the stress relaxation layer also decreases, and therefore, the stress relaxation layer can be easily formed. However, when the winding pitch decreases, the amount of used superconducting wire increases, leading to an increase in cost, and therefore, it is important to choose the winding step as much as possible limiting the increase in the amount of used superconducting wire. Therefore, by limiting the ratio of the winding pitch to the diameter of the winding, as described above, it is possible to obtain a superconducting cable with a short pitch capable of reducing the amount of compression in diameter when the superconducting wire is compressed during cooling, and with a step also relatively limiting the amount of superconducting wire used. A particularly preferred step of winding the superconducting wire is 5 times the diameter of the winding.

[0034] A preferred winding pitch of the superconducting wire can be calculated as follows. First, we study the relationship between the ratio "(pitch / diameter)" of the winding pitch to the winding diameter of the superconducting wire constituting the superconducting layer and the compression ratio in diameter when the superconducting wire is cooled. The relationship between the “ratio (pitch / diameter)” and the amount of superconducting wire used is then examined. Next, a winding pitch and a winding diameter of the superconducting wire are selected, capable of making the compression amount in the diameter of the superconducting wire equal to or less than the average value for the modulus, and capable of making the amount of used superconducting wire equal to or less than the average value for the modulus.

[0035] Otherwise, a coil holding layer may be formed on the outside of the superconducting layer. When forming the holding layer of the coils on the outer side of the superconducting layer, an operation of attaching the superconducting layer to the inner side can be expected. Using the attachment operation, the compression of the superconducting layer in diameter can proceed smoothly. The material of the holding layer of the coils may be formed by a material capable of giving a predetermined attachment force to the superconducting layer, for example, preferably a metal tape, in particular a copper tape or the like, can be used.

[0036] When a winding holding layer is used, it is also preferable to place a cushioning layer between the winding holding layer and the superconducting layer. When a metal tape is used for the hold-up layer, usually also silver metal or the like. is used for the superconducting wire, and therefore, a contact is formed between the metals between the coil holding layer and the superconducting layer, and there is a possibility of damage to the superconducting wire. Therefore, when a cushioning layer is placed between the two layers, damage to the superconducting wire can be prevented by eliminating direct metal contact. As a specific material of the cushioning layer, insulating paper or carbon paper may preferably be used.

[0037] In addition, it is preferable to provide a protective layer on the outermost periphery of the cable core. The protective layer is given the function of mechanical protection of the outer conductor layer and insulation from the heat-insulating pipe. As the material of the protective layer, insulating paper from kraft paper or the like, or plastic tape can be used.

[0038] On the other hand, a heat insulating pipe can be formed using any structure, provided that the structure is a structure capable of supporting thermal insulation of the refrigerant. For example, the location of the heat insulating element between the twin pipes of a double structure containing the outer pipe and the inner pipe, and the evacuation of the gap between the inner pipe and the outer pipe are noted. Usually between the inner pipe and the outer pipe is superinsulation obtained by laminating a metal foil and a plastic mesh. At least a conductor layer is contained in the inner space of the inner pipe, and it is filled with refrigerant in the form of liquid nitrogen or the like. to cool this conductor layer.

[0039] The refrigerant may maintain the superconducting wire in a superconducting state. At present, it is most practical to use liquid nitrogen as a refrigerant, but otherwise it is possible to use liquid helium, liquid hydrogen, or the like. In particular, in the case of liquid nitrogen, a cable can be formed that insulates with a liquid in which polypropylene does not swell, and is excellent in the withstand DC voltage characteristic or the impulse withstand voltage Imp. Even when the insulating layer consists of a composite tape with a high value k, i.e., having a greater thickness of polypropylene.

[0040] The present invention is applicable to superconducting DC and AC cables. In particular, it is preferable to apply the present invention to a superconducting DC cable in which the limitation of the winding pitch of the superconducting wire in the superconducting layer is negligible, as described above. However, even in the case of an AC cable, for example, (1) when the conductor layer and the shielding layer are respectively formed by single layers, (2) when the conductor layer and the shielding layer are formed by several layers, the need to adjust the pitch is negligible and preference is given to countermeasures thermal compression, a short step can be taken as the step of winding a superconducting wire. Therefore, even in the case of an AC cable, a thermal compression absorption mechanism can be imparted to the cable core itself.

The results of the invention

[0041] According to the superconducting cable of the invention, the following results can be achieved.

[0042] (1) By providing a stress relaxation layer on the inner side of the superconducting layer when the superconducting wire is compressed by cooling, at least a portion corresponding to a compression amount in the diameter of the superconducting layer corresponding to this compression can be absorbed by the stress relaxation layer. Therefore, the operation of the superconducting wire under excessive tension can be excluded, and the decrease in the superconducting characteristic can be limited.

[0043] (2) The absorption mechanism of thermal compression can be performed in the cable core itself with a simple structure by providing a stress relaxation layer on the inner side of the superconducting layer. Therefore, it is not necessary to use a large-scale structure with sliding of the peripheral end portion of the cable or the like, making the structure capable of reliably absorbing the thermal compression amount of the superconducting wire.

[0044] (3) By providing a thermal compression absorption mechanism in the cable core itself, the compression amount of the superconducting wire can be absorbed not only in the multi-core superconducting cable, but also in the single-core superconducting cable, which was considered difficult to provide for a conventional absorption mechanism.

[0045] (4) By providing a stress relaxation layer absorbing a compression amount of the diameter of the outer conductor layer by the insulating layer per se, there is no need to re-form the stress relaxation layer for the outer conductor layer, and the increase in the cable diameter can be restrained.

[0046] (5) By providing the winding step of the superconducting wire 4-6 times larger than the diameter of the winding, a superconducting cable can be formed that can absorb the amount of compression of the superconducting wire with a simple structure, and also can reduce the amount of used superconducting wire as much as possible .

[0047] (6) By providing a winding-retaining layer on the outer side of the superconducting layer, the compression in diameter can be smoothly absorbed by the stress relaxation layer by pressing the superconducting layer against the inner peripheral side, which makes the compression flow in diameter smoothly in accordance with the thermal compression of the superconducting wire.

Brief Description of the Drawings

[0048] [Fig. 1] Fig. 1 is a sectional view of a superconducting cable according to the invention.

[FIG. 2] FIG. 2 is a graph showing a relationship between a “ratio (pitch / diameter)” and a compression amount in diameter when cooling a superconducting wire.

[Fig. 3] Fig. 3 is a graph showing the relationship between the “ratio (pitch / diameter)” and the amount of superconducting wire used.

[Figure 4] Figure 4 is a sectional view of a conventional superconducting cable according to the prior art.

Description of reference numbers and symbols

[0049] 100 DC superconducting cable

10 core, 11 wireframe, 12 inner side stress relaxation layer, 13 conductor layer, 14A, 14B shock absorbing layers, 15A, 15B coil-holding layers, 16 insulating layer / outer stress relaxation layer, 16A insulating layer, 17 return line conductor, 17A shielding layer, 18 protective layer, 20 heat-insulating pipe, 21 inner pipe, 22 outer pipe, 23 corrosion-resistant layer

The best embodiment of the invention

[0050] An embodiment of the invention will be explained as follows.

[0051] (Option 1)

[Whole structure]

As shown in FIG. 1, the superconducting DC cable 100 according to the invention consists of a single cable core 10 and a heat-insulating pipe 20 containing this core 10.

[0052] [Vein]

The core 10 sequentially from its center includes the frame 11, the inner side stress relaxation layer 12, the conductor layer 13, the shock absorbing layer 14A, the coil-holding layer 15A, the insulating layer (also the outer stress relaxation layer) 16, the outer conductor layer (conductor 17 (reverse line), a shock absorbing layer 14B, a coil holding layer 15B and a protective layer 18.

[0053] <Frame>

To perform the frame 11, a corrugated stainless steel tube is used. When a hollow framework 11 is used, its interior may be a channel for the flow of refrigerant (in this case, liquid nitrogen).

[0054] <Layer of stress relaxation of the inner side>

An inner side stress relaxation layer 12 is formed by winding the PPLP composite tape (registered trademark) manufactured by Sumitomo Denki Kogyo K.K. onto the frame 11, formed by laminating kraft paper and a polypropylene film. In this case, a material and its thickness are selected that can absorb the amount of compression in diameter when cooling the conductor layer 13 indicated below. More specifically, PPLP is used with a ratio k of the thickness of the polypropylene film to the thickness of the entire composite tape equal to 60%.

[0055] <Conductor Layer>

To perform the conductor layer 13, a ribbon wire with a Bi2223 phase in an Ag-Mn sheath is used, having a thickness of 0.24 mm and a width of 3.8 mm. A conductor layer 13 is formed by winding such a ribbon wire onto the inner side stress relaxation layer 12 in several layers. In this case, the superconducting wire is wound on it in 4 layers.

[0056] <Cushioning layer and hold-up layer>

The cushioning layer 14A is formed on the conductor layer 13, and then the coils holding layer 15A is formed on it. The cushion layer 14A is formed by winding several layers of kraft paper onto the conductor layer, and the coil holding layer 15A is formed by winding the copper tape. The cushioning layer 14A prevents contact between the metals of the conductor layer and the coil-holding layer 15A, and the coil-holding layer 15A smoothly compresses the diameter of the conductor layer 13 upon cooling by attaching the conductor layer 13 to the inner peripheral side via the cushioning layer 14A.

[0057] <The insulating layer / outer layer of stress relaxation>

An insulating layer 16 is formed on the coil holding layer 15A. In this case, the insulating layer 16 is formed by PPLP with a k value of 60%. The insulating layer 16 is given the function of electrical insulation of the conductor layer 13, and also the function of the outer layer of stress relaxation to absorb the compression value in diameter in accordance with the cooling of the outer conductor layer indicated below. When the outer stress relaxation layer is formed by the insulating layer 16 itself, it is not necessary to separately form the outer stress relaxation layer, and therefore, the increase in the outer diameter of the cable core can be limited.

[0058] Furthermore, although not shown, the inner peripheral side of the insulating layer is formed with the inner semiconducting layer, and its outer peripheral side is formed with the outer semiconducting layer. Any of these semiconducting layers is formed by winding carbon paper.

[0059] <Outer conductor layer (return conductor)>

An outer conductor layer (return line conductor 17) is provided on the outside of the insulating layer 16. In the case of direct current, a path for return current is required, and therefore, for a single-pole power transmission, a return line conductor 17 is used as a path for return current. The return line conductor 17 is formed from the superconducting wire like a conductor layer 13 and has a transmission capacity similar to that of the conductor layer 13.

[0060] <Cushioning layer and coil holding layer>

Then, an absorbing layer 14B is formed on the outer conductor layer, and then a coil holding layer 15B is formed on it. The cushion layer 14B and the coil holding layer 15B are formed from materials similar to the materials of the cushion layer 14A and the coil holding layer 15A provided on the outside of the conductor layer 13. The cushion layer 14B prevents contact between the metals of the return line conductor 17 and the coil holding layer 15B and makes smooth flow of compression in the diameter of the return line conductor 17 by attaching the return line conductor 17 to the inner peripheral side by means of a cushioning layer 14B.

[0061] <Protective layer>

The outer side of the return line conductor 17 is provided with a protective layer 18 formed of an insulating material. In this case, the protective layer 18 is formed by winding kraft paper. By means of the protective layer 18, the return conductor 17 can be mechanically protected, the heat insulating pipe (inner pipe 21) can be insulated, and bypass current back to the heat insulating pipe 20 can be prevented.

[0062] <Thermal Insulation Pipe>

The heat insulating pipe 20 comprises twin pipes, including the inner pipe 21 and the outer pipe 22, and a vacuum heat insulating layer is formed between these inner and outer pipes 21, 22. Inside the vacuum insulating layer is the so-called superinsulation, formed by laminating a plastic mesh and metal foil. The space formed between the inner side of the inner pipe 21 and the core 10 is a channel for the flow of refrigerant. In addition, a corrosion resistant layer 23 can be formed on the outer periphery of the heat insulating pipe 20 using polyvinyl chloride or the like. as needed.

[0063] (Example of a test calculation)

Then, in the manufacture of the superconducting cable, the following test calculation is carried out so that the amount of used superconducting wire can be made as small as possible, while bearing in mind the formation of a short pitch of the superconducting wire so that the compression value in diameter can be made as small as possible.

[0064] First, a relationship is studied between the ratio of the winding pitch and the winding diameter of the superconducting wire constituting the superconducting layer, the “ratio (pitch / diameter)”, and the compression amount of the diameter of the superconducting wire. In this case, the diameter of the winding is formed in 3 ways: 20 mm 30, 30 mm ⌀, 40 mm и, and the diameter compression value, when the superconducting wire is compressed by 0.3% when cooling during operation, is calculated using the linear expansion coefficients of the corresponding materials . The calculation result is shown in the graph of figure 2.

[0065] As shown in this graph, when the “ratio (pitch / diameter)” remains the same, it is known that the larger the diameter of the winding, the smaller the compression ratio of the diameter. In addition, it is also known that when the diameter of the winding remains the same, the smaller the "ratio (pitch / diameter)", the smaller the compression ratio of the diameter. It can be seen from the result that the diameter compression amount to be absorbed is smaller when a short pitch is selected.

[0066] Then, the relationship between the “ratio (pitch / diameter)” and the amount of superconducting wire used was investigated. In this case, the amount of used superconducting wire when the superconducting wire is located along the longitudinal direction of the wrapped object, that is, when the superconducting wire is positioned longitudinally in line, is 1.0, and it is shown how the amount of used superconducting wire changes when the ratio (pitch / diameter ) "varies in relative magnitude. The result of this is shown in the graph of FIG. 3.

[0067] As shown in the graph, it can be seen that although the amount of used superconducting wire does not increase very much up to a “ratio (pitch / diameter)” of about 6.0, the amount of used superconducting wire rapidly increases when this ratio becomes smaller, than 4.0.

[0068] From these two results of the test calculation, it is clear that the “ratio (pitch / diameter)” can be made approximately 4.0 to 6.0, when the compression ratio of the superconducting wire during cooling is brought to an easily absorbed level, and also small amount of used superconducting wire.

[0069] Table 1 summarizes the constituent materials and dimensions of the respective parts of the superconducting cable (50 kV, 10,000 A) according to the invention, constructed based on the result of the test calculation. In addition, the steps of winding the superconducting wires of the conductor layer and the outer conductor layer are 5 times larger than the winding diameters. Namely, the steps are 210 mm in the conductor layer and about 274 mm in the outer conductor layer.

[0070]

[Table 1] constituent element material outer diameter (mm), etc. frame stainless steel corrugated tube thirty stress relaxation layer of the inner side Pplp 42 (thickness: 6 mm) conductor layer superconducting wire with phase Bi2223 46.4 (4 layers) cushioning layer / coil holding layer kraft paper / copper tape 47.4 insulation layer / stress relaxation layer Pplp 54.7 (thickness: 3 mm) outer conductor layer superconducting wire with phase Bi2223 57.5 (3 layers) cushioning layer / coil holding layer kraft paper / copper tape 59.5 protective layer kraft paper 61.7 (thickness 1 mm) cable outer diameter 116

[0071] In the structure according to table 1, the diameter of the frame as such is also compressed during cooling. When it is given a compression ratio of 0.3%, the compression ratio of the frame diameter becomes 0.09 mm. On the other hand, the compression ratio of the diameter of the superconducting wire with a compression ratio of 0.3% is 0.45 mm under conditions of a winding diameter of 42 mm and a winding pitch of 210 mm. Therefore, it is seen that only 20% of the compression of the diameter of the conductor layer can be absorbed by the compression of the diameter of the frame. Therefore, it can be seen that when the compression ratio of the diameter of the stress relaxation layer of the inner side is 0.36 mm, 100% of the compression of the diameter of the conductor layer can be absorbed by the total compression of the diameter of the carcass and the relaxation layer of the stresses of the inner side. In addition, it is seen that when the stress relaxation layer of the inner side has a compression diameter of 0.45 mm, the total compression of the diameter of the conductor layer can be absorbed only by the stress relaxation layer of the inner side.

[0072] Although an explanation is given in detail and with reference to a specific embodiment, it will be apparent to one skilled in the art that the invention may be modified or modified without departing from the spirit and scope of the invention.

In addition, this application is based on the Japanese Patent Application (Japanese Patent Application No. 2004-350327), filed December 2, 2004, and its contents are hereby incorporated by reference.

Industrial applicability

[0073] The superconducting cable according to the invention can be used as an electric power transmission means. In particular, the superconducting cable according to the invention can preferably be used as a single-core means for transmitting direct current electricity.

Claims (9)

1. A superconducting cable comprising a superconducting wire constituting a superconducting layer by spiral winding; and a stress relaxation layer provided in the cable core on the inner side of the superconducting layer, wherein the compression amount in the direction of the diameter of the superconducting layer in accordance with the cooling of the superconducting wire with the refrigerant is absorbed by the stress relaxation layer. 2. The superconducting cable according to claim 1, further comprising a cable constituent element provided on the inner side of the stress relaxation layer, wherein a compression amount in the direction of the diameter of the superconducting layer in accordance with the cooling of the superconducting wire with the refrigerant is absorbed by the stress relaxation layer and the cable constituent element. 3. The superconducting cable according to claim 1, wherein the superconducting layer includes a conductor layer, and the stress relaxation layer includes an inner side stress relaxation layer formed on the inner side of the conductor layer. 4. The superconducting cable according to claim 3, in which the insulating layer provided on the outer side of the conductor layer is used as the stress relaxation layer of the outer side in the stress relaxation layer, and the superconducting layer includes an outer conductor layer formed on the outer side insulating layer. 5. The superconducting cable according to claim 1, wherein the step of winding the superconducting wire is 4-6 times larger than the diameter of the winding of the superconducting wire. 6. The superconducting cable according to claim 1, in which the cable constituent element includes a frame, and this frame is either a corrugated tube or a spiral ribbon-shaped element. 7. The superconducting cable according to claim 1, wherein the stress relaxation layer is formed by at least one of kraft paper, plastic tape and a composite tape of kraft paper and plastic tape. 8. The superconducting cable according to claim 1, further comprising a coil-holding layer on the outside of the superconducting layer. 9. The superconducting cable according to any one of claims 1 to 8, and this superconducting cable is a superconducting DC cable.

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